Driving circuit for a shared sense amplifier

ABSTRACT

When any one of memory cells (MC 1R , MC NR  and MC 1L , MC NL ) connected with respective bit lines (3 R , 4 R  and 3 L , 4 L ) is addressed, the gate potential of a transfer transistor group (7 R , 8 R  or 7 L , 8 L ) connected with the bit lines on the non-selected side is clamped at bit line precharge voltage, whereby the said transfer transistor group (7 R , 8 R  or 7 L , 7 L ) is turned off. Thus, the bit lines on the non-selected side are cut off at a high speed from a sense amplifier.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a driving circuit for a shared sense amplifier, and more particularly, it relates to a circuit for driving a sense amplifier shared by two pairs of folded bit lines or open bit lines at a high speed.

2. Description of the Prior Art

FIG. 1 shows an example of a shared sense amplifier to which the present invention can be applied. In FIG. 1, a clock φ₃ is supplied to respective sources of transistors 1 and 2. The drain of the transistor 1 is connected to a sense node 9 while the gate thereof is connected to a sense node 10. On the other hand, the drain of the transistor 2 is connected to the sense node 10 while the gate thereof is connected to the sense node 9. These transistors 1 and 2 form a flip-flop type sense amplifier.

The sense node 9 is connected to a bit line 3_(R) through a transfer transistor 7_(R) and to a bit line 3_(L) through a transfer transistor 7_(L). The sense node 10 is connected to a bit line 4_(R) through a transfer transistor 8_(R) and to a bit line 4_(L) through a transfer transistor 8_(L). The transfer transistors 7_(R) and 8_(R) are adapted to connect and cut off the bit lines 3_(R) and 4_(R) on the right side with and from the sense amplifier, and are on-off controlled by a control clock φ_(2R). Similarly, the transfer transistors 7_(L) and 8_(L) are adapted to connect and cut off the bit lines 3_(L) and 4_(L) on the left side with and from the sense amplifier, and are on-off controlled by a control clock φ_(2L). The bit lines 3_(R) and 4_(R) form a pair of folded bit lines while the bit lines 3_(L) and 4_(L) similarly form another pair of folded bit lines. In the shared sense amplifier circuit as shown in FIG. 1, the sense amplifier, which is formed by the transistors 1 and 2, is shared by the two pairs of folded bit lines.

The bit lines 3_(R) and 4_(R) on the right side of FIG. 1 are respectively connected with sources of transistors 5_(R) and 6_(R). Precharge voltage V_(R) is applied to respective drains of the transistors 5_(R) and 6_(R) while a precharge clock φ_(1R) is supplied to respective gates thereof. These transistors 5_(R) and 6_(R) are adapted to charge the bit lines 3_(R) and 4_(R) at the precharge voltage V_(R) in response to the precharge clock φ_(1R) respectively. The bit lines 3_(R) and 4_(R) are further connected with memory cells MC_(1R) and MC_(NR) respectively. The storage content of the memory cell MC_(1R) is read on the bit line 3_(R) when a word line WL_(1R) is selected while the storage content of the memory cell MC_(NR) is read on the bit line 4_(R) when a word line WL_(NR) is selected. The bit lines 3_(R) and 4_(R) are further connected with dummy memory cells DC_(1R) and DC_(2R). With respect to the dummy memory cell DC_(1R), intermediate potential between read out potential of information "0" and that of information "1" is read on the bit line 3_(R) when a dummy word line DWL_(1R) is selected, while the said intermediate potential is read on the bit line 4_(R) when a dummy word line DWL_(2R) is selected with respect to the dummy memory cell DC_(2R).

Elements similar to those connected with the bit lines 3_(R) and 4_(R) are connected with the bit lines 3_(L) and 4_(L) in the left-hand direction. The elements corresponding to the aforementioned ones are indicated by the same reference numerals, except for that the subscripts "R" are replaced by "L", and detailed description thereof is herein omitted.

The bit lines 3_(L) and 4_(L) on the left side are connected with read/write lines I/O₁ and I/O₂ respectively through transfer transistors 11 and 12. A clock φ₄ is supplied to respective gates of the transfer transistors 11 and 12.

Although merely four word lines WL_(1R),WL_(NR), WL_(1L) and WL_(NL) are shown in FIG. 1, a number N (arbitrarily selected even number) of word lines are present on each side in practice while of the corresponding number N of memory cells MC_(1R) (MC_(1L)) to MC_(NR) (MC_(NL)), N/2 are connected with the bit lines 3_(R) (3_(L)) and 4_(R) (4_(L)), respectively.

Although the circuit as shown in FIG. 1 employs only one sense amplifier, a practical memory is generally formed by a plurality of sense amplifiers which are vertically aligned to form arrays of memory cells.

Description is now made on a circuit having one sense amplifier and two word lines, for easy understanding of the present invention.

FIG. 2 is a timing chart of an NMOS employed for illustrating the operation of the circuit as shown in FIG. 1.

In a standby state to a time T₁, the precharge clock φ_(1L) is at a high level, whereby the transistors 5_(L) and 6_(L) are in ON states and the bit lines 3_(L) and 4_(L) are charged at the precharge voltage V_(L). The precharge clock φ_(1R) is also at a high level, whereby the bit lines 3_(R) and 4_(R) are charged at the precharge voltage V_(R) through the transistors 5_(R) and 6_(R). During this period, the clock φ₃ for inactivating the sense amplifier is at a high level, whereby the sense amplifier is retained in the standby state. Assuming here that either of the memory cells MC_(1R) and MC_(NR) on the right side of the sense amplifier is addressed by address data (not shown), the potential of either word line WL_(1R) or WL_(NR) and that of either dummy word line DWL_(1R) or DWL_(2R) are increased, while the non-selected word line WL_(1L) or WL_(NL) and dummy word line DWL_(1L) or DWL_(2L) remain at low levels.

The potential levels at the selected word line and dummy word line are not immediately increased upon the addressing performed by the address data. This is because the address data are supplied to a decoder (not shown), which increases the potential levels at the selected word line and dummy word line, whereby the increase in the potential levels of the word line and dummy word line is delayed from the addressing by the time required for processing in the decoder.

Description is now made on the case where, for example, the word line WL_(1R) and dummy word line DWL_(2R) are selected.

Upon input of the address data, the control clock φ_(2L) is turned to a low level at a time T₂ before increase of the potential levels at the word line WL_(1R) and dummy word line DWL_(2R), whereby the transfer transistors 7_(L) and 8_(L) are both made nonconductive. Thus, the sense nodes 9 and 10 are electrically cut off from the bit lines 3_(L) and 4_(L), and the potential levels at the word line WL_(1R) and dummy word line DWL_(2R) are increased at a time T₃. Then, information stored in the memory cell MC_(1R) is read on the bit line 3_(R) and the charge stored in the dummy memory cell DC_(2R) is read on the bit line 4_(R) respectively. The read information is transferred to the sense nodes 9 and 10 through the transfer transistors 7_(R) and 8_(R) during the period when the control clock φ_(2R) is at a high level to a time T₄. The level of the control clock φ_(2R) slightly drops at the time T₄ while impedance levels of the transfer transistors 7_(R) and 8_(R) are increased. When the clock φ₃ is turned to a low level at a time T₅, the sense amplifier formed by the transistors 1 and 2 is activated and the information transferred to the sense nodes 9 and 10 is amplified. The amplified information is returned to the bit lines 3.sub. R and 4_(R) respectively through the transfer transistors 7_(R) and 8_(R), to be re-written in the memory cell being selected. The control clock φ_(2L) is again turned to a high level at a time T₆, whereby the amplified information is transferred to the bit lines 3_(L) and 4_(L) through the transfer transistors 7_(L) and 8_(L).

The clock φ₄ is turned to a high level at a time T₇, and the amplified information is transferred to the read/write lines I/O₁ and I/O₂ through the transfer transistors 11 and 12. The word line WL_(1R), dummy word line DWL_(2R) and clock φ₄ return to low levels at a time T₈ and the clocks φ_(1R), φ_(1L), φ₃ and φ_(2R) are turned to high levels at a time T₉, whereby the folded bit lines on both sides are oharged at V_(R) and V_(L) respectively, and the sense amplifier returns to a standby state.

The sequential read/write operation is performed in the aforementioned manner. The impedance levels of the transfer transistors 7_(R) and 8_(R) are so increased in amplification of the sense amplifier as to reduce capacity loads at the sense nodes 9 and 10 thereby to increase amplification sensitivity.

When the memory cells MC_(1L) and MC_(NL) on the left side are selected, the waveforms of the control clocks φ_(2L) and φ_(2R) change places with each other.

As hereinabove described, the sense amplifier as shown in FIG. 1 is driven to be shared by two pairs of folded bit lines.

As obvious from the foregoing description, the waveforms of the control clocks φ_(2R) and φ_(2L) have important functions for driving the shared sense amplifier. Particularly the control clock on the non-selected side (φ_(2L) in the above case) must be immediately turned to a low level before the potential levels at the selected word lines rise upon the addressing of the memory cells by the address data, i.e., before read-out of the memory cells, to cut off the non-selected bit lines from the sense amplifier. Slow fall of the control clock on the non-selected side delays the read-out from the memory cells, whereby high-speed read-out is disabled. The slow fall of the control clock further delays transfer of the information amplified by the sense amplifier to the read/write lines I/O₁ and I/O₂, whereby the high-speed read-out is disabled. Thus, there is needed an implementation of a driving circuit for a shared sense amplifier which can attain high-speed read-out operation by quickly connecting and cutting off bit lines with and from the sense amplifier.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a driving circuit for a sense amplifier shared by two pairs of bit lines which can connect and cut off the bit lines with and from the sense amplifier at a high speed thereby to drive the shared sense amplifier at a high speed.

Briefly stated, the present invention provides a circuit for driving at a high speed a shared sense amplifier including two pairs of bit lines respectively connected with memory cells, a sense amplifier positioned between the two pairs of bit lines for amplifying information read from the memory cells, a first transfer transistor group interposed between one of the pairs of bit lines and the sense amplifier and a second transfer transistor group interposed between the other pair of bit lines and the sense amplifier thereby to share the sense amplifier by the two pairs of bit lines, and the driving circuit comprises a clamp clock generation circuit, a decoder and an on-off control means. The clamp clock generation circuit is adapted to generate a clamp clock which responds at a high speed to addressing of the memory cells, and the decoder is adapted to decode the clamp clock from the clamp clock generation circuit while the on-off control means is adapted to control on-off operations of the first and second transfer transistor groups on the basis of the output from the decoder. The on-off control means includes a clamp means for clamping upon addressing of either of the memory cells the gate potential of the transfer transistor group interposed between the bit lines in the area not connected with the addressed memory cell and the sense amplifier at bit line precharge voltage thereby to turn off the said transfer transistor group.

Generated according to the present invention is the clamp clock which responds at a high speed to the addressing to produce a control clock from the clamp clock, thereby to control on-off operations of the first and second transfer transistor groups by the control clock, and hence the bit lines on the non-selected side can be cut off from the sense amplifier immediately upon the addressing of the memory cell. In order to turn off the first or second transfer transistor group, the gate voltage at the transfer transistor group is not completely turned to a low level but clamped at the bit line precharge voltage, whereby the time required for cutting off the transfer transistor group can be reduced in comparison with the case where the gate voltage thereof is completely turned to a low level, and the cut off operation can be performed at a higher speed. Therefore, even if the time interval from the addressing of the memory cell to actual readout of the information in the memory cell is extremely short, the bit lines on the non-selected side can reliably be cut off from the sense amplifier within the short interval, thereby to attain high-speed driving of the shared sense amplifier.

Further, the gate voltage of the transfer transistor group is clamped at the bit line precharge voltage as hereinabove described so that the said transfer transistor group is automatically turned on by the amplification function of the sense amplifier to re-connect the bit lines on the non-selected side with the sense amplifier, and hence such re-connection can be performed at a higher speed in comparison with the case where voltage is applied to the gate of the transfer transistor group after the operation of the sense amplifier to re-connect the bit lines on the non-selected side with the sense amplifier. Therefore, the content of the memory cell can be externally read immediately after termination of the operation of the sense amplifier, thereby to attain high-speed readout operation.

The above and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing an example of a shared sense amplifier to which the present invention can be applied;

FIG. 2 is a timing chart for illustrating the general operation for driving the circuit as shown in FIG. 1;

FIG. 3 is a timing chart for illustrating the driving operation according to an embodiment of the present invention;

FIG. 4 is a circuit diagram showing a part of the embodiment of the present invention, particularly a circuit for generating control clocks;

FIG. 5 is a timing chart for illustrating the operation of the circuit as shown in FIG. 4;

FIG. 6 is a circuit diagram showing another part of the embodiment of the present invention, particularly a circuit for generating clamp clocks;

FIG. 7 is a timing chart for illustrating the operation of the circuit as shown in FIG. 6;

FIG. 8 is a circuit diagram showing still another part of the embodiment of the present invention, particularly a decode circuit for decoding the clamp clocks outputted from the circuit as shown in FIG. 6 to that shown in FIG. 4;

FIG. 9 is a timing chart for illustrating the operation of the circuit as shown in FIG. 8;

FIG. 10 is a circuit diagram showing a further part of the embodiment of the present invention, particularly a circuit for generating clocks for driving the circuit as shown in FIG. 4; and

FIG. 11 is a timing chart for illustrating the operation of the circuit as shown in FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3 is a timing chart for illustrating the operation performed by an embodiment of the present invention for driving a shared sense amplifier. The basic circuit structure of the shared sense amplifier may be identical to that shown in FIG. 1. In a standby state, precharge clocks φ_(1L) and φ_(1R) are both at high levels and hence bit lines 3_(R), 4_(R), 3_(L) and 4_(L) are charged respectively at precharge voltage levels V_(R) and V_(L). The voltage levels V_(R) and V_(L) are generally set equal to each other, and hence they are hereafter indicated as V_(REF). At this time, the levels of control clocks φ_(2L) and φ_(2R) are set higher than the total of the bit line precharge voltage V_(REF) and threshold voltage of transfer transistors. Therefore, all of the transfer transistors 7_(L), 8_(L), 7_(R) and 8_(R) are in ON states whereby sense nodes 9 and 10 are precharged at V_(REF). The feature of this driving method resides in that the level of a control clock 100 _(2L) on the non-selected side is not completely turned to a low level, but clamped at the bit line precharge voltage V_(REF) before rise of corresponding word lines upon addressing of memory cells. In other words, the bit lines 3_(R), 3_(L), 4_(R) and 4_(L) and sense nodes 9 and 10 are at the potential level of V_(REF), and hence the transfer transistors 7_(L) and 8_(L) are cut off with drains, sources and gates being at the same level by clamping the control clock φ_(2L) at V_(REF). As a matter of course, such cut-off operation can be performed by clamping the level of the control clock φ_(2L) at V_(REF) at a higher speed than the case where the same is turned to a low level.

For example, when a memory cell MC_(1R) storing low level charge is addressed, the operation is performed in the following manner: In FIG. 3, symbols V_(3R) and V_(3L) indicate potential levels at the bit lines 3_(R) and 3_(L) respectively, while symbol V₉ indicates the potential level at the sense node 9. At a time T₁, precharge clocks φ_(1R) and φ_(1L) are turned to low levels, while the potential levels V_(3R) and V_(3L) remain at V_(REF). At a time T₂, the control clock φ_(2L) is clamped at V_(REF), whereby the transfer transistors 7_(L) and 8_(L) are turned off as hereinabove described and the bit line 3_(L) is electrically cut off from the sense node 9. On the other hand, the control clock φ_(2R) remains at a high level, whereby the bit line 3_(R) remains connected with the sense node 9. At a time T₃, the potential at a word line WL_(1R) is increased and the information in the memory cell MC_(1R) is read on the bit line 3_(R). At this time, the potential V_(3R) at the bit line 3_(R) is slightly lowered by a level determined by the capacitance ratio of the memcry cell MC_(1R) to the bit line 3_(R). The potential at the sense node 9 is slightly lowered in response to this, whereas the transfer transistor 7_(L) is not turned on since the decreased level is generally smaller than a threshold voltage V_(TH) of the transistors. At a time T₅, the clock φ₃ is turned to a low level thereby to activate the sense amplifier, and the potential level V₉ at the sense node 9 begins to be lowered. At this time, the control clock φ_(2R) is lowered to V_(REF) and the bit line 3_(R) is temporarily cut off from the sense node 9, whereby the capacitive load is reduced and the amplification sensitivity is improved. After a lapse of a time ΔT from the time T₅, the potential level V₉ reduced to (V_(REF) -V_(TH)), whereby the transfer transistors 7_(L) and 7_(R) begin to enter ON states and the bit lines 3_(L) and 3_(R) are automatically re-connected with the sense node 9. Thereafter the control clocks φ_(2R) and φ_(2L) are turned to high levels, i.e., levels higher than V_(REF) at a time T₆, whereby the transfer transistors 7_(R) and 7_(L) are increased in conductivity. Therefore, the information read from the memory cell is sufficiently transmitted to read/write lines in the read-out operation.

As hereinabove described, the bit lines on the non-selected side are cut off from the sense amplifier by clamping the gate voltage of the transfer transistors on the non-selected side at the bit line precharge voltage before rise of potential levels at the word lines upon addressing of the memory cell in the aforementioned operation, whereby attained is a cut-off operation at a higher speed than the case where the gate voltage levels at the transfer transistors are completely turned to low levels. Further, the gate voltage levels at the transfer transistors are so clamped at the bit line precharge voltage level that the transfer transistors are automatically turned on by the amplification function of the sense amplifier and the bit lines on the non-selected side are automatically re-connected with the sense amplifier, whereby the time required for the re-connection of the bit lines on the non-selected side is extremely reduced. Therefore, the content of the memory cell can be outputted to the exterior immediately after the amplification by the sense amplifier, thereby to enable high-speed readout operation. Further, the gate voltage levels at the transfer transistors are made to be higher than the total of the bit line precharge voltage and the threshold voltage levels of the transfer transistors for reading the content of the memory cell to attain a sufficient read-out level in the aforementioned embodiment, and the rise of the gate voltage in this case can be performed in a shorter period than that in the case where the gate voltage levels of the transfer transistors are completely turned to low levels to be then turned to high levels. Thus, such a point also contributes to the high-speed read-out operation.

Description is now made of an example of structure of a driving circuit required for attaining the operation as shown in FIG. 3. In the following description, the bit line precharge voltage V_(REF) is assumed to be equal to supply voltage V_(CC).

FIG. 4 shows a circuit for generating the control clock φ_(2L) as shown in FIG. 3. The circuit as shown in FIG. 4 includes transistors Q₁ to Q₈ and capacitors C₁ to C₅. The drain of the transistor Q₁ receives the supply voltage V_(CC) and the gate receives the precharge clock φ_(1L) while the source is connected to a node N₂. The drain of the transistor Q₂ receives an inverted precharge clock φ_(1L) which is an inverted signal of the precharge clock φ_(1L), while the gate receives the supply voltage V_(CC) and the source is connected to the node N₁. The drain of the transistor Q₃ receives the supply voltage V_(CC) and the gate is connected to the node N₁ while the source is connected to the node N₂. The drain of the transistor Q₄ receives the supply voltage V_(CC) and the gate is connected to the node N₂ while the source is connected to an output terminal 13, which is adapted to output the control clock φ_(2L). The drain of the transistor Q₅ receives the supply voltage V_(CC) and the gate is connected to a node N₃ while the source is connected to the output terminal 13. The drain of the transistor Q₆ receives the supply voltage V_(CC) and the gate is connected to a node N₄ while the source is connected to the node N₃. The drain of the transistor Q₇ receives the inverted precharge clock φ_(1L) and the gate receives the supply voltage V_(CC) while the source is connected to the node N₄. The drain of the transistor Q₈ receives the supply voltage V_(CC) and the gate receives the precharge clock φ_(1L) while the source is connected to the node N₃. One end of the capacitor C₁ is connected to the node N₁ while the other end thereof receives in inverted delayed clock φ₃ ', which is an inverted delayed signal of a clock φ₃. One end of the capacitor C₂ is connected to the node N₂ and the other end thereof receives a clamp clock φ_(5L) which is hereinafter described in detail. One end of the capacitor C₃ is connected to the output terminal 13, while the other end thereof receives a clock φ_(6L) which is also hereinafter described. One end of the capacitor C₄ is connected to the node N₃ while the other end thereof receives the inverted clock φ₃ which is the inverted signal of the clock φ₃. One end of the capacitor C₅ is connected to the node N₄, while the other end thereof receives the inverted delayed clock φ₃ '.

A circuit for generating the control clock φ_(2R) is in similar structure to the circuit for generating the control clock φ_(2L), except that a precharge clock φ_(1R) and an inverted precharge clock φ_(1R) are supplied in place of the precharge clock φ_(1L) and inverted precharge clock φ_(1L) and a clamp clock φ_(5R) is supplied in place of the clamp clock φ_(5L) while a clock φ_(6R) is supplied in place of the clock φ_(6L).

FIG. 5 is a timing chart for illustrating the operation of the circuit as shown in FIG. 4. Referring now to FIG. 5, the following description is provided of the operation of the circuit as shown in FIG. 4, in the case where the memory cell on the right side of the sense amplifier is addressed as shown in FIG. 1.

In the standby state to the time T₁, the precharge clock φ_(1L) and clock φ₃ are at high levels, and the output terminal 13 and, thus, the control clock φ_(2L) are precharged at higher levels than the supply voltage V_(CC) by capacitive coupling of the capacitor C₃ as hereinafter described. At this time, the nodes N₂ and N₃ are precharged at the supply voltage V_(CC) by turning-on of the transistors Q₁ and Q₈, whereas the transistors Q₄ and Q₅ remain in OFF states since the potential levels at the sources thereof are higher than those of the gates. Further, the inverted precharge clock φ_(1L) is at a low level, and hence the nodes N₁ and N₄ are at low levels through the transistors Q₂ and Q₇ respectively. Therefore, both of the transistors Q₃ and Q₆ are in OFF states.

At the time T₁, the precharge clock φ_(1L) is turned to a low level and the inverted precharge clock φ_(1L) is turned to a high level, whereby the nodes N₁ and N₄ are turned to high levels through the transistors Q₂ and Q₇. Then, at the time T₂, the clamp clock φ_(5L) is turned to a high level whereby the node N₂ is boosted by capacitive coupling of the capacitor C₂ to a level sufficiently higher than the supply voltage V_(CC). Therefore, the transistor Q₄ is strongly turned on and the control clock φ_(2L) is clamped at a high speed from the high level exceeding the supply voltage V_(CC) to the level of the supply voltage V_(CC). At the same time, the clock φ_(6L) is also turned to a low level, whereby the level of the control clock φ_(2L) is pulled in a low level to be clamped at the level of the supply voltage V_(CC) at a higher speed by capacitive coupling of the capacitor C₃. At the time T₅, the clock φ₃ is turned to a low level and the inverted clock φ₃ is turned to a high level whereby the node N₃ is boosted to a level sufficiently higher than the supply voltage V_(CC) by capacitive coupling of the capacitor C₄. Thus, the transistor Q₅ is strongly turned on, whereas no change takes place since the control clock φ_(2L) is already clamped at the level of the supply voltage V_(CC) in this case. At a time T₅ ', the inverted delay clock φ₃ ' is turned to a high level whereby the nodes N₁ and N₄ are boosted by levels sufficiently higher than the supply voltage V_(CC) by capacitive coupling of the capacitors C₁ and C₅. Therefore, the transistors Q₃ and Q₆ are strongly turned on and the nodes N₂ and N₃ are clamped at the level of the supply voltage V_(CC), whereby the transistors Q₄ and Q₅ are turned off. Then, at the time T₆, the clock φ_(6L) is again turned to a high level, whereby the control clock φ_(2L) is turned to a high level exceeding the supply voltage V_(CC) by capacitive coupling of the capacitor C₃.

On the other hand, in the circuit for generating the control clock φ_(2R) , the clamp clock φ_(5R) remains at a low level and the clock φ_(6R) remains at a high level at the time T₂, and hence the node N₂ remains at the level of the supply voltage V_(CC) and the control clock φ_(2R) remains at the high level exceeding the supply voltage V_(CC). At the time T₅, the inverted clock φ₃ is turned to a high level and the clock φ_(6R) is turned to a low level, whereby the transistor Q₅ is strongly turned on by the capacitor C₄ to clamp the control clock φ_(2R) at the level of the supply voltage V_(CC). Such clamping is made at a higher speed by the function of the capacitor C₃. The operation thereafter is substantially identical to that of the circuit for generating the control clock φ_(2L).

In the case where the memory cell on the left side of the sense amplifier as shown in FIG. 1 is addressed, the operation of the circuit for generating the control clock φ_(2L) is simply by that of the circuit for generating the control clock φ_(2R).

As hereinabove described, the control clocks φ_(2L) and φ_(2R) which can drive the shared sense amplifier as shown in FIG. 1 at a high speed, are obtained by the circuit as shown in FIG. 4.

Description is now made on an example of structure of a circuit for generating the clamp clock φ_(5L) (φ_(5R)) supplied to the circuit as shown in FIG. 4. This clamp clock generation circuit is formed by two portions of a φ₅ generation circuit for generating a clamp clock φ₅ in high-speed response to the addressing of the memory cells by the address data and a decode circuit for decoding the clamp clock φ₅ thereby to generate two types of clamp clocks φ_(5L) and φ_(5R).

FIG. 6 is a circuit diagram showing definite arrangement of the aforementioned circuit for generating the clamp clock φ₅. In FIG. 6, the φ₅ generation circuit includes transistors M₁ to M₁₁ and a capacitor C₆. The drain of the transistor M₁ receives the supply voltage V_(CC) and the gate receives the precharge clock φ₁ while the source is connected to the node N₅. The drain of the transistor M₂ is connected to the node N₅ and the gate receives a first address clock φ_(A) while the source is grounded. The drain of the transistor M₃ is connected to the node N while the gate receives a second address clock φ_(A) and the source is grounded. The drain of the transistor M₄ receives an inverted precharge clock φ₁ which is an inverted signal of the precharge clock φ₁ and the gate is connected with the node N₅ while the source is connected with by node N₆. The drain of the transistor M₅ is connected with the node N₆ and the gate receives the inverted delayed clock φ₃ ' while the source is grounded. The drain of the transistor M₆ receives the supply voltage V_(CC) and the gate is connected to the node N₆ while the source is connected to a node N₇. The drain of the transistor M₇ is connected with the node N₇ while the gate receives the inverted delayed clock φ₃ ' and the source is grounded. The drain of the transistor M₈ is connected with the node N₇ and the gate is connected with the node N₅ while the source thereof is grounded. The drain of the transistor M₉ receives the supply voltage V_(CC) while the gate is connected with the node N₇ and the source is connected with an output terminal 14, which outputs the clamp clock φ₅. The drain of the transistor M₁₀ is connected with the output terminal 14 and the gate is connected with the node N₅, while the source is grounded. The drain of the transistor M₁₁ is connected with the output terminal 14, while the gate receives the inverted delayed clock φ₃ ', and the source is grounded. One end of the capacitor C₆ is connected with the node N₆ and the other end thereof is connected with the node N₇.

Either of the precharge clocks φ_(1L) and φ_(1R) as shown in FIG. 1 may serve as the precharge clock φ₁. Alternatively, an address strobe signal may be employed in place of the precharge clock φ₁. Further, the first and second address clocks φ_(A) and φ_(A) ' are formed by partial bits extracted from the address data for addressing the memory cell, and the first address clock φ_(A) indicates addressing of the memory cell on the right side of the sense amplifier in FIG. 1 while the second address clock φ_(A) indicates addressing of of the memory cell on the left side of the sense amplifier in FIG. 1. In other words, the first address clock φ_(A) is turned to a high level when the memory cell on the right side is addressed while the second address clock φ_(A) is turned to a high level when the memory cell on the left side is addressed.

FIG. 7 is a timing chart for illustrating the operation of the circuit as shown in FIG. 6. The operation of the circuit in FIG. 6 is now described with reference to FIG. 7. In the standby state to the time T₁, the precharge clock φ₁ is at a high level and the node N₅ is precharged at a high level through the transistor M₁. Therefore, the transistors M₄, M₈ and M₁₀ are in ON states and the nodes N₆ and N₇ and clamp clock φ₅ are at low levels. At the time T₁, the precharge clock φ₁ is turned to a low level and the inverted precharge clock φ₁ is turned to a high level whereby the transistor M₁ is turned off while the node N₅ remains at a high level, and hence the transistor M₄ is retained in an ON state. Therefore, the high-level inverted precharge clock φ₁ is supplied to the node N₆, which is turned to a high level whereby the transistor M₆ is turned on. However, since the node N₅ remains at a high level, the transistor M₈ is retained in an ON state and the node N₇ is retained at a low level. At the time T₂, either the first or second address clock φ_(A) or φ_(A) is turned to a high level whereby either the transistor M₂ or M₃ is turned on to turn the node N₅ to a low level. Therefore, the transistor M₄ is turned off and the node N₆ enters a high floating state. On the other hand, the transistors M₈ and M₁₀ are turned off whereby the level of the node N₇ begins to be increased. Then the node N₆ is boosted to a higher level by capacitive coupling of the capacitor C₆, whereby the transistor M₆ is strongly turned on to increase the voltage at the node N₇ to the level of the supply voltage V_(CC) at a high speed. Thus, the transistor M₉ is turned on to turn the clamp clock φ₅ to a high level at a high speed. Then, at the time T₆, the inverted delayed clock φ₃ ' is turned to a high level, whereby the transistors M₅, M₇ and M₁₁ are turned on to turn the nodes N₆ and N₇ and clamp clock φ₅ to low levels. Although the inverted delayed clock φ₃ ' is employed in this embodiment to reset the circuit, such reset operation may be performed by other types of reset clocks.

According to the circuit of FIG. 6 as hereinabove described, generated is the clamp clock φ₅ which responds at a high speed to the first or second address clock φ_(A) or φ_(A).

FIG. 8 shows an example of the aforementioned decode circuit, particularly a circuit for producing the clamp clock φ_(5L). The circuit as shown in FIG. 8 includes transistors M₁₂ to M₁₈. The drain of the transistor M₁₂ receives the supply voltage V_(CC) while the gate receives the precharge clock φ₁ and the source is connected with a node N₈. The drain of the transistor M₁₃ is connected to the node N₈ while the gate receives a second address clock φ_(A) and the source is grounded. The drain of the transistor M₁₄ receives the clamp clock φ₅ from the circuit as shown in FIG. 6 while the gate is connected with the node N₈ and the source is connected with an output terminal 15, which outputs the clamp clock φ_(5L). The drain of the transistor M₁₅ is connected with the output terminal 15 and the gate is connected with a node N₉ while the source is grounded. The drain of the transistor M₁₆ receives the supply voltage V_(CC) and the gate receives the precharge clock φ₁ while the source is connected with node N₉. The drain of the transistor M₁₇ is connected with the node N₉ and the gate is connected with the output terminal 15 while the source is grounded. The drain of the transistor M₁₈ is connected with the output terminal 15 while the gate receives a clamp clock φ_(5R) and the source is grounded.

A circuit for producing the clamp clock φ_(5R) (similarly included in the decode circuit) is in similar structure to the aforementioned circuit as shown in FIG. 8, except that the first address clock φ_(A) is supplied in place of the second address clock φ_(A) and the clamp clock φ_(5L) is supplied in place of the clamp clock φ_(5R).

FIG. 9 is a timing chart for illustrating the operation of the circuit as shown in FIG. 8. The operation of the circuit in FIG. 8 is now described with reference to FIG. 9, on such case that the memory cell on the right side of the sense amplifier in FIG. 1 is addressed.

In the standby state to the time T₁, the precharge clock φ₁ is at a high level. Therefore, the transistors M₁₂ and M₁₆ are in ON states and the nodes N₈ and N₉ are precharged at high levels. Thus, the transistors M₁₄ and M₁₅ are turned on and the output terminal 15 and, thus, the clamp clock φ_(5L) are at low levels. If the memory cell on the right side in FIG. 1 is addressed at the time T₂, the first address clock φ_(A) is turned to a high level while the second address clock φ_(A) remains at a low level. Therefore, the node N₈ is retained at a high level at the time T₂, thereby to retain the transistor M₁₄ in an ON state. Thus, the level of the clamp clock φ₅ is directly transmitted to the output terminal 15, and the clamp clock φ_(5L) presents the same waveform as that of the clamp clock φ₅. At this time, the transistor M₁₇ is turned on to turn the node N₉ to a low level, whereby the transistor M₁₅ is in an OFF state.

On the other hand, in the circuit for producing the clamp clock φ_(5R), the first address clock φ_(A) rises to a high level at the time T₂, whereby the transistor M₁₃ is turned on and the node N₈ is turned to a low level while the transistor M₁₄ is cut off. Thus, the level of the clamp clock φ₅ is not transmitted to the output terminal 15, and the transistor M₁₇ is not turned on. Therefore, the transistor M₁₅ remains in an ON state and the clamp clock φ_(5R) is retained at a low level. Further, during the period when the clamp clock φ_(5L) is at a high level, the transistor M₁₈ is in an ON state whereby the clamp clock φ_(5R) is securely retained at a low level state at least in the high-level period of the clamp clock φ_(5L).

In the case where the memory cell on the left side of the circuit as shown in FIG. 1 is selected, the operation of the circuit for producing the clamp clock φ_(5L) is simply replaced by the operation of that for producing the clamp clock φ_(5R).

Description is now made on an example of structure of a circuit for generating the clock φ_(6L) supplied to the circuit as shown in FIG. 4. FIG. 10 shows the circuit for generating the clock φ_(6L). The circuit as shown in FIG. 10 includes transistors M₁₉ to M₂₇. The drain of the transistor M₁₉ receives the supply voltage V_(CC) and the gate receives the precharge clock φ₁ while the source is connected to a node N₁₀. The drain of the transistor M₂₀ is connected with the node N₁₀ while the gate receives the inverted delayed clock φ₃ ' and the source is grounded. The drain of the transistor M₂₁ receives the inverted clock φ₃ while the gate is connected with the node N₁₀ and the source is connected with a node N₁₁. The drain of the transistor M₂₂ is connected with the node N₁₁ while the gate receives the inverted delayed clock φ₃ ' and the source is grounded. The drain of the transistor M₂₃ is connected with the node N₁₁ while the gate receives the precharge clock φ₁ and the source is grounded. The drain of the transistor M₂₄ receives the supply voltage V_(CC) and the gate receives the precharge clock φ₁ while the source is connected with an output terminal 16, which outputs the clock φ_(6L). The drain of the transistor M₂₅ receives the supply voltage V_(CC) and the gate receives an inverted delayed clock φ₃ " and the source is connected with the output terminal 16. The drain of the transistor M₂₆ is connected with the output terminal 16 and the gate is connected with the node N₁₁ while the source is grounded. The drain of the transistor M₂₇ is connected with the output terminal 16 while the gate receives the clamp clock φ_(5L) and the source is grounded.,

The inverted delayed clock φ₃ " is obtained by delaying the inverted delayed clock φ₃ ' further by a prescribed time.

On the other hand, a circuit for generating the clock φ_(6R) is in similar arrangement to that of the circuit as shown in FIG. 10, except that the clamp clock φ_(5R) is supplied in place of the clamp clock φ_(5L).

FIG. 11 is a timing chart for illustrating the operation of the circuit as shown in FIG. 10. The operation of the circuit in FIG. 10 is now described with reference to FIG. 11.

In the standby state to the time T₁, the precharge clock φ₁ is at a high level and all of the transistors M₁₉, M₂₃ and M₂₄ are in ON states. Therefore, the node N₁₀ is at a high level and the node N₁₁ is at a low level, while the output terminal 16 and, thus, the clock φ_(6L) are at high levels. At the time T₁, the precharge clock φ₁ is turned to a low level, whereby all of the transistors M₁₉, M₂₃ and M₂₄ are turned off while all of the nodes N₁₀ and N₁₁ and output terminal 16 enter floating states and no change is caused in the potential levels. At the time T₂, the clamp clock φ_(5L) is turned to a high level, whereby the transistor M₂₇ is turned on to turn the output terminal 16 to a low level, whereby the clock φ_(6L) is turned to a low level. Then, at the time T₅, the clock φ₃ is turned to a low level and the inverted clock φ₃ is turned to a high level, and since the node N₁₀ is at a high level, the node N₁₁ is turned to a high level through the transistor M₂₁. Therefore, the transistor M₂₆ is turned on, while no change is caused in the clock φ _(6L) since the output terminal 16 is already at a low level. At the time T₅ ', the inverted delayed clock φ₃ ' is turned to a high level and the clamp clock φ_(5L) is turned to a low level whereby the transistors M₂₀ and M₂₂ are turned on and the transistor M₂₇ is turned off. Therefore, the nodes N₁₀ and N₁₁ are turned to low levels, whereby the transistors M₂₁ and M₂₆ are turned off. At the time T₆, the inverted delayed clock φ₃ " is turned to a high level, whereby the transistor M₂₅ is turned on to again turn the output terminal 16 to a high level. Therefore, the clock φ_(6L) is turned to a high level.

On the other hand, in the circuit for generating the clock φ_(6R), the clamp clock φ_(5R) remains at a low level at the time T₂, and hence the clock φ_(6R) remains at a high level. At the time T₅, the inverted clock φ₃ is turned to a high level, whereby the transistor M₂₆ is turned on to turn the output terminal 16 and, thus, the clock φ_(6R) to low levels. The operation thereafter is substantially identical to that of the circuit as shown in FIG. 10.

According to the circuit of FIG. 10 as hereinabove described, generated is the clock φ_(6L) (φ6R) required for driving the circuit as shown in FIG. 4.

The driving circuit for a shared sense amplifier according to the embodiment of the present invention is formed by the aforementioned circuits as shown in FIGS. 4, 6, 8 and 10, thereby to generate the control clock φ_(2L) (φ_(2R)) which can drive the shared sense amplifier at a high speed.

Although the aforementioned description has been made on a shared sense amplifier employing folded bit lines, open bit lines may be employed in place of the same. In this case, the bit lines 3_(L) and 3_(R) in FIG. 1 are taken as a pair of open bit lines and the bit lines 4_(L) and 4_(R) are taken as another pair of open bit lines while a clock corresponding to the control clock φ_(2L) is inputted in the gates of the transfer transistors 7_(L) and 7_(R) and a clock corresponding to the control clock φ_(2R) is inputted in the gates of the transfer transistors 8_(L) and 8_(R). Alternatively, the bit lines 3_(L) and 4_(R) may be taken as a pair of open bit lines while taking the bit lines 3_(R) and 4_(L) as another pair of open bit lines and inputting a clock corresponding to the control clock φ_(2R) in the gates of the transfer transistors 7_(L) and 8_(R) and a clock corresponding to the control clock φ_(2R) in the gates of the transfer transistors 8_(L) and 7_(R).

Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims. 

What is claimed is:
 1. A driving circuit for a shared sense amplifier which drives at a high speed a shared sense amplifier circuit including two pairs of it lines (3_(R), 4_(R) and 3_(L), 4_(L)) respectivey connected with memory cells (MC_(1R) , MC_(NR) and MC_(1L), MC_(NL)), a sense amplifier (1, 2) provided between said two pairs of bit lines for amplifying information read from said memory cells, a first transfer transistor group (7_(R), 8_(R) or 7_(L), 8_(L)) interposed between one of said pairs of bit lines (3_(R), 4_(R) or 3_(L), 4_(L)) and said sense amplifier and a secnd transfer transistor group (7_(L), 8_(L) or 7_(R), 8_(R)) interposed between the other pair of bit lines (3_(L), 4_(L) or 3_(R), 4_(R)) and said sense amplifier (1, 2) thereby to share said sense amplifier by said two pairs of bit lines (3_(R), 4_(R) and 3_(L), 4_(L)), said driving circuit comprising:a clamp clock generation circuit for generating a clamp clock (φ₅) respondig at a high speed to addressing of said memory cells; a decoder for decoding said clamp clock (φ₅); and on-off control means for controlling on-off operations of said first and second transfer transistor groups on the basis of an output from said decoder, said on-off control means including clamp means for clamping, upon addressing of any one of said memory calls, the gate voltage of said transfer transistor group interposed between the pair of bit lines not connected with said addressed memory cell and said sense amplifier, said gate voltage equal to the precharge voltage of said bit lines thereby to turn off said transfer transistor group.
 2. A driving circuit for a shared sense amplifier in accordance with claim 1, wherein said on-off control means includes means for setting, in a standby state before said addressing of said memory cells, the gate voltage levels of respective transfer transistor groups to be higher than a respectie total of precharge voltage levels of said bit lines and threshold voltage levels of said transfer transistor groups thereby to turn on said respective transfer transistor groups.
 3. A driving circuit for a shared sense amplifier in accordance with claim 1, wherein said two pairs of bit lines are formed by folded bit lines (3_(R), 4_(R) and 3_(L), 4_(L)) respectively.
 4. A driving circuit for a shared sense amplifier in accordance with claim 1, wherein said two pairs of bit lines are formed by open bit lines respectively.
 5. A driving circuit for a shared sense apmplifier in accordance with claim 1, wherein said clamp clock generation circuit includes:a first potential level source (V_(cc)), a second potential level (ground) source having a potential level different from that of said first potential level source, a first transistor (M₆) having a first conducting terminal connected with said first potential level source, a second transistor (M₈) interposed between a second conducting terminal of said first transistor and said second potential level source, first circuit means (M₁ -M₄) for making said first transistor conductive and said second transistor non-conductive in response to said addressing of said memory cell, boostsing capacitor means (C₆) inerposed between said second conducting terminal of said first transistor and the gate terminal of said first transistor for making said first transistor conductive at a high speed, and second circuit means (M₉) for producing said clamp clock (φ₅) on the basis of change in potential at said second conducting terminal of said first transistor.
 6. A driving circuit for a shared sense amplifier in accordance with claim 1, wherein said on-off control means includes first transistor means connected to the precharge voltage of said bit lines and responsive to a precharge clock signal for said bit lines, further transistor means responsive to clock signals for activating and deactivating the sense amplifier, and output transistor means responsive to said further transistor means and to said first transitor means for outputting a control clock signal for controlling operations of said first and second transfer transistor groups.
 7. A driving circuit for a shared sense amplifier in accordance with claim 6, wherein said output transistor means comprises a pair of parallel connected transistors having gates connected to outputs of said first transistor means, a first of said pair of output transistors connected to said clamp clock signal and operable or responding to initiation of said clamp clock signal to clamp the transfer transistor groups for the nonselected bit lines to said precharge voltage level, thereby to turn off said transfer transistor group,a second of said pair of putput transistors connected to said clock signals for said sense amplifier and operable in response to said clock signals for sais sense amplifier to continue to clamp said transfer transistor group to said precharge voltagae after termination of said clamp clock signal.
 8. A driving circuit for a shares sense amplifier in accordance with claim 7, wherein said further transistor means is connected to receive a delayed invereted form of said clock signal for said sense amplifier and operable in response thereto for providing to said output transistors a gate signal for turning off said output transistors.
 9. A driving circuit for a shared sense amplifier in accordance with claim 8, further comprising means responsive to a level raising clock signal for providing to the gates of said transfer transistor group a voltage level for turning on said transfer transistor group subsequent to turning off of said output transistors.
 10. In a driving circuit for a shared sense amplifier which drives at a high speed a shared sense amplifier circuit including two pairs of bit lines (3_(R), 4_(R) and 3_(L), 4_(L)) respectively connected with memory cells (MC_(1R) , MC_(NR) and MC_(1L), MC_(NL)), a sense amplifier (1, 2) provided between said two pairs of bit lines for amplifying information read from said memory cells, a first transfer transistor group (7_(R), 8_(R) or 7_(L), 8_(L)) interposed between one of said pairs of bit lines (3_(R), 4_(R) or 3_(L), 4_(L)) and said sense amplifier and a second transfer transistor group (7_(L), 8_(L) or 7_(R), 8_(R)) interposed between the other pair of bit lines (3_(L), 4_(L) or 3_(R), 4_(R)) and said sense amplifier (1, 2) thereby to share said sense amplifier by said two pairs of bit lines (3_(R), 4_(R) and 3_(L), 4_(L)), the improvemet comprising:on-off control means for controlling on-off operations of said first and second transfeer transistor groups based on an output from a decoder for decoding a clamp clock signal, said on-off control means including clamp means, operable upon addressing of one of said memory cells, connected to said sense amplifier by one pair of bit lines, for disconnecting from the sense amplifier the other pair of bit lines connected between a non-addressed memory cell and the sense amplifier, said claiming means operable for disconnecting the other pair of bit lines by clamping the gate voltage of the transfer transistor group connecting the other pair of bit lines to the sense amplifier too the precharge voltage level for the bit lines. 